1. Field of the Invention
This invention relates to sample handling devices, and more particularly to a device for introducing samples into sample chambers of a test instrument.
2. Background Information
Chemical analysis of liquids, including biological liquids such as blood, plasma or urine is often desirable or necessary. Sensors that utilize various analytical elements to facilitate liquid analysis are known. These elements have often included components which specifically react to a substance or characteristic under analysis, termed analyte herein. These components, upon contacting a liquid sample containing the analyte, effect formation of a colored or fluorescent material or another detectable response to the presence of the analyte.
In this regard, analytical elements such as disclosed in commonly assigned U.S. patent application Ser. No. 08/617,714 (hereinafter, the '714 Patent Application) have been provided. Analytical elements of this type are adapted for use within a sample chamber of an optical sensor assembly. In operation, a fluid sample of unknown analyte content (an “unknown sample”) is tested by introducing the sample into the sample chamber where it contacts the analytical element. Any change in the optical characteristics of the analytical element are observed to thus determine characteristics of the analyte of interest in the sample. An example of a sensor assembly of this type is disclosed in commonly assigned U.S. patent application Ser. No. 09/010,096, entitled “OPTICAL SENSOR AND METHOD OF OPERATION” (hereinafter referred to as the “OPTICAL SENSOR” patent application) which is hereby incorporated by reference in its entirety, herein. The sample chambers of this and similar types of sensor assemblies are generally incorporated into multiple use clinical instrumentation which utilize a sample introduction device, including an aspiration probe, to withdraw a sample, such as blood or other fluid, from a syringe or the like and transfer the sample into the sample chamber. An example of instrumentation that utilizes an aspiration probe to withdraw a sample is disclosed in commonly assigned U.S. patent application Ser. No. 60/006,741, entitled “MULTIFUNCTION VALVE” filed on Nov. 2, 1995.
In this type of instrumentation, once the tip of the aspiration probe is immersed within the syringe, a suction pump draws blood through the probe and into the instrument. As the blood sample flows from the syringe, its volume is replaced by air that passes through an opening in the coupling between the syringe and the instrument, and through an annular space between the probe and the opening of the syringe.
While multiple use instruments that draw blood in this manner may operate satisfactorily in many applications, they present some difficulties. In particular, the sample introduction device, including the inside of the aspiration probe, must be routinely cleaned between samples to prevent clogs and cross contamination of the samples. Although blood gas sample syringes are treated with an anti-coagulant, blood samples often contain micro-clots which can block the narrow flow passages of sample introduction devices of analytical instrumentation. In many current blood gas analyzers, such as the Rapidpoint 400 sold by Bayer Corporation of Medfield, Mass., problems associated with these clots are minimized by providing the inlet of the sample aspiration probe with the smallest diameter of the entire sample flow path through the sample introduction device. If a clog does occur, it is likely to be at the tip of the probe and can be cleared by wiping or flushing. However, the inclusion of probe washing facilities complicates the fluidics of a clinical analyzer. Moreover, the washing sequence is time consuming and disadvantageously reduces the availability of the instrument for sample analysis. Such delay may be particularly disadvantageous in some operating environments such as, for example, in critical care facilities.
Further, discarded wash fluid or reagent comprises a significant portion of the waste generated by such conventional analytical instrumentation. This waste is classified as biohazardous and thus disposal thereof is relatively expensive, both in economic and environmental terms. This waste also poses a potential health risk to health care workers and those who may otherwise come into contact with the waste during or after disposal.
Thus, a need exists for an improved sample introduction device that reduces the need for washing between samples to reduce the amount of reagent required therefor and that otherwise overcomes the drawbacks of the prior art.